Dr. Tom Way CSC 4181 Slide 1
CSC 4181 – Compiler Construction
Software Engineering Lectures
Part 2
Dr. Tom Way CSC 4181 Slide 2
Software Requirements
Dr. Tom Way CSC 4181 Slide 3
Requirements engineering
zThe process of establishing the services that the
customer requires from a system and the
constraints under which it operates and is
developed.
zThe requirements themselves are the
descriptions of the system services and
constraints that are generated during the
requirements engineering process.
Dr. Tom Way CSC 4181 Slide 4
What is a requirement?
zIt may range from a high-level abstract statement
of a service or of a system constraint to a
detailed mathematical functional specification.
zThis is inevitable as requirements may serve a
dual function
• May be the basis for a bid for a contract - therefore
must be open to interpretation;
• May be the basis for the contract itself - therefore
must be defined in detail;
• Both these statements may be called requirements.
Dr. Tom Way CSC 4181 Slide 5
Types of requirement
zUser requirements
• Statements in natural language plus diagrams of the
services the system provides and its operational
constraints. Written for customers.
zSystem requirements
• A structured document setting out detailed
descriptions of the system’s functions, services and
operational constraints. Defines what should be
implemented so may be part of a contract between
client and contractor.
Dr. Tom Way CSC 4181 Slide 6
Functional and non-functional requirements
zFunctional requirements
• Statements of services the system should provide, how the
system should react to particular inputs and how the system
should behave in particular situations.
zNon-functional requirements
• constraints on the services or functions offered by the system
such as timing constraints, constraints on the development
process, standards, etc.
zDomain requirements
• Requirements that come from the application domain of the
system and that reflect characteristics of that domain.
